Max PLATE current for a 572-B is 275 ma. per tube, maximum
grid current is 50 ma. per tube. In a properly operating SB-200 you'll
see 500 ma plate current keydown, about 85-100 ma grid current and
2000 volts HV at about 600-650 watts output 80-15 meters and about
450-500 watts out on 10 meters with about 80-90 watts of drive.
The zero signal plate idle current should be about 80 - 100 ma.
A good thing to do with these amps is to make sure the 200 pf
grid bypass caps have the SHORTEST possible lead lengths even if you
have to rearrange the ground lugs. I would also place a pair of
cross-connected
silicon diodes acrossed the meter movement. Very SLIGHTLY bending the
N.O.
output contact on the T-R relay up will ensure that the output contact
"makes" before
the input contact thus preventing hot switching the output contacts.
Mark WB8JKR
On Sat, 14 Jun 2003 22:54:16 -0400 "George & Marijke Guerin"
<gmguerin@voyager.net> writes:
> Hi Jeff, etc.,
>
> I lost one of those resistors many years ago. I would say old age.
> Maybe
> some stray current, but I replaced the 33 ohm 1W with 33 ohm 2 Watt
> resistors. One of my tubes was not working with the 33 ohm resistor
> blown.
> The other was bright orange, taking all the load. You may have one
> tube
> either cut off or "floating along". I do not remember if I was
> getting 300
> or 500 watts when this happened. By the way, I was on 40 phone and
> happened
> to stand up and look down on the amp, and saw one tube bright orange
> and one
> black.
>
> If you are getting 500+ watts out and an indication of only 200 ma
> plate
> current, I would also look at the plate current resistors, R12 and
> R14 and
> make sure the plate meter is reading close to 500 ma. R12 could be
> low or
> R14 could be high or both.
> The grid current at 500 ma plate current should be about 150 ma.
> Look up
> the current data sheets by Svetlana or similar on line. My old ARRL
> handbook
> does not give grid current for grounded grid operation, just 500 ma
> max for
> a pair and 600 watts out for 1100 to 1200 watts input.
>
> Good luck, George K8GG
>
>
> ----- Original Message -----
> From: "Jeff Stewart" <stewgoat@indy.net>
> To: "amps" <amps@contesting.com>
> Sent: Friday, June 13, 2003 9:18 PM
> Subject: [Amps] Sb-200 plate current (again)
>
>
> > I just did a visual and a 33 ohm resister off the grid of one
> tube
> R21 or R22 is cracked in two. The tube on that side has a
> discoloration on
> one side (the gitter appears to be at the bottom) so it may be
> toast. Now
> to figure cause and effect I guess before I replace the resistor.
> Suggestions?
> >
> > Jeff
>
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